Yea I'm almost positive the manual says straight 30, not 10w 30. Also I was told that regular automotive oil does not perform very well in these engines bc they are not made to try and keep engine temps down, since cars have radiators and mowers don't. But then again that came from my old dealer who never really told the truth. Exmark makes Premium Oil which is suppose to keep engine temps low which would improve the condition and life span of your engine.